When using transcutaneous nerve stimulators for pain control and body function stimulation, sudden increases in output current to the patient, via the electrodes used with these stimulators, have been known to occur. These surges in output current can result in discomfort, skin burns, muscle spasms, and pain and fright to a patient. With weak or sensitive patients or with patients with cardiac conditions these results can be dangerous or even disastrous.
Often, these sudden increases in output current are the result of intermittent electrode connections, improper unit operation, surges within the unit due to circuitry failures or intermittent power supply connections. These types of surge generating conditions, especially where the stimulator units are operated by the patients themselves, can never be completely controlled or eliminated.
My pending patent application Ser. No. 634,577 discloses a fault protection circuit for monitoring the pulse output of a stimulator to disable the stimulator's pulse generator when the current level of the output pulses increases at an excessive rate. This type circuit will detect electrode reconnect after disconnect which occurs while the stimulator is "on". Even though this fault circuit reacts very quickly to disable the stimulator, this circuit cannot eliminate altogether the electrical shock received by the patient upon electrode reconnect.
Moreover, this previous circuit used many components to sample and hold output pulses before differentiating to feed a threshold detector.
An object of this invention, therefore is to provide an improved circuit connectable to exising stimulator circuitry for detecting output load disconnect.
Another object of this invention is to provide an improved circuit for detecting excessively high load impedance.
Another object of the invention is to provide a simple and economical circuit to monitor surges in output current level.
A further object of the invention is to provide a circuit for disabling the output pulse generator within the stimulator unit when any of the undesirable conditions is detected.
An additional object of this invention is to provide the detection and control circuitry which will tolerate certain acceptable ramps normally present during stimulator adjustment.